diff --git a/src/lib/Makefile.am b/src/lib/Makefile.am
index 7419bedf9..91327cdf5 100644
--- a/src/lib/Makefile.am
+++ b/src/lib/Makefile.am
@@ -19,6 +19,17 @@ libcin3_a_srcdir = $(top_srcdir)/src/lib
 noinst_LIBRARIES += libcin3.a
 
 libcin3_a_CFLAGS = $(CFLAGS) -std=gnu99 -Wall -Werror
+libcin3_a_CPPFLAGS = -I$(top_srcdir)/src/
+
+libcin3_a_SOURCES = \
+	$(libcin3_a_srcdir)/plugin.c \
+	$(libcin3_a_srcdir)/error.c \
+	$(libcin3_a_srcdir)/time.c \
+	$(libcin3_a_srcdir)/framerate.c
+
+noinst_HEADERS += \
+	$(libcin3_a_srcdir)/plugin.h \
+	$(libcin3_a_srcdir)/error.h \
+	$(libcin3_a_srcdir)/time.h \
+	$(libcin3_a_srcdir)/framerate.h
 
-libcin3_a_SOURCES = $(libcin3_a_srcdir)/plugin.c $(libcin3_a_srcdir)/error.c
-noinst_HEADERS += $(libcin3_a_srcdir)/plugin.h $(libcin3_a_srcdir)/error.h 
diff --git a/src/lib/framerate.c b/src/lib/framerate.c
new file mode 100644
index 000000000..138a338a3
--- /dev/null
+++ b/src/lib/framerate.c
@@ -0,0 +1,25 @@
+/*
+  framerate.c  -  framerate calculations
+
+  Copyright (C)         CinelerraCV
+    2007,               Christian Thaeter <ct@pipapo.org>
+
+  This program is free software; you can redistribute it and/or
+  modify it under the terms of the GNU General Public License as
+  published by the Free Software Foundation; either version 2 of the
+  License, or (at your option) any later version.
+
+  This program is distributed in the hope that it will be useful,
+  but WITHOUT ANY WARRANTY; without even the implied warranty of
+  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+  GNU General Public License for more details.
+
+  You should have received a copy of the GNU General Public License
+  along with this program; if not, write to the Free Software
+  Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
+*/
+
+#include "lib/error.h"
+
+CINELERRA_ERROR_DEFINE(FRAMERATE_ILLEGAL_TIME, "invalid time given");
+CINELERRA_ERROR_DEFINE(FRAMERATE_ILLEGAL_FRAME, "invalid frame given");
diff --git a/src/lib/framerate.h b/src/lib/framerate.h
new file mode 100644
index 000000000..2df5971fb
--- /dev/null
+++ b/src/lib/framerate.h
@@ -0,0 +1,103 @@
+/*
+  framerate.h  -  framerate calculations
+
+  Copyright (C)         CinelerraCV
+    2007,               Christian Thaeter <ct@pipapo.org>
+
+  This program is free software; you can redistribute it and/or
+  modify it under the terms of the GNU General Public License as
+  published by the Free Software Foundation; either version 2 of the
+  License, or (at your option) any later version.
+
+  This program is distributed in the hope that it will be useful,
+  but WITHOUT ANY WARRANTY; without even the implied warranty of
+  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+  GNU General Public License for more details.
+
+  You should have received a copy of the GNU General Public License
+  along with this program; if not, write to the Free Software
+  Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
+*/
+
+#ifndef CINELERRA_FRAMERATE_H
+#define CINELERRA_FRAMERATE_H
+
+#include <limits.h>
+
+#include "lib/error.h"
+#include "lib/time.h"
+
+/**
+ * framerates are defined as a rational number
+ * for example NTSC with 30000/1001fps
+ */
+struct cinelerra_framerate_struct
+{
+  unsigned n; //numerator
+  unsigned d; //denominator
+};
+
+typedef struct cinelerra_framerate_struct cinelerra_framerate;
+typedef cinelerra_framerate* CinelerraFramerate;
+
+typedef signed long cinelerra_framepos;
+
+CINELERRA_ERROR_DECLARE(FRAMERATE_ILLEGAL_TIME);
+CINELERRA_ERROR_DECLARE(FRAMERATE_ILLEGAL_FRAME);
+
+#define CINELERRA_FRAMEPOS_ERROR LONG_MIN
+
+/**
+ * Get the frame number of a given time at a given frame rate.
+ * frame indexing starts with 1
+ * @param framerate is a pointer to the framerate used, defined as rational number. Must be given.
+ * @param time is a pointer to a cinelerra_time which shall be converted.
+ * @return frame at the given time or CINELERRA_FRAMEPOS_ERROR on error.
+ */
+static inline cinelerra_framepos
+cinelerra_framerate_frame_get_time (const CinelerraFramerate framerate, CinelerraTime time)
+{
+  REQUIRE (framerate);
+  if (!time || time->tv_sec == (time_t)-1)
+    {
+      cinelerra_error_set(CINELERRA_ERROR_FRAMERATE_ILLEGAL_TIME);
+      return CINELERRA_FRAMEPOS_ERROR;
+    }
+
+  /* we add a magic microsecond for rounding, because of integer truncation frames may be calculated at most 1us earlier,
+     the idea is to compensate odd framerates which fall out off microsecond precision.
+   */
+  return ((time->tv_sec * 1000000ULL + time->tv_usec + /*magic*/1) * framerate->n)/(framerate->d * 1000000ULL) + 1;
+}
+
+/**
+ * Get the start time for a frame.
+ * frame indexing starts with 1
+ * @param framerate is a pointer to the framerate used, defined as rational number. Must be given.
+ * @param time is a pointer to a cinelerra_time which shall take the result.
+ * @param frame frame number to be converted to time. This frame number must be greater than 0.
+ * @return the pointer given in time or NULL on error (or when it was given as time).
+ */
+static inline CinelerraTime
+cinelerra_framerate_time_get_time_frame (const CinelerraFramerate framerate,
+                                         CinelerraTime time,
+                                         cinelerra_framepos frame)
+{
+  REQUIRE (framerate);
+  if (time)
+    {
+      if (frame < 1)
+        {
+          cinelerra_error_set(CINELERRA_ERROR_FRAMERATE_ILLEGAL_FRAME);
+          return NULL;
+        }
+
+      unsigned long long usec = ((frame-1) * framerate->d * 1000000ULL - (/*magic*/frame>1?1:0)) / framerate->n;
+
+      time->tv_sec = usec / 1000000;
+      time->tv_usec = usec % 1000000;
+    }
+  return time;
+}
+
+#endif
diff --git a/src/lib/time.c b/src/lib/time.c
new file mode 100644
index 000000000..6cbdde6ee
--- /dev/null
+++ b/src/lib/time.c
@@ -0,0 +1,26 @@
+/*
+  time.h  -  Time and frame calculations
+
+  Copyright (C)         CinelerraCV
+    2007,               Christian Thaeter <ct@pipapo.org>
+
+  This program is free software; you can redistribute it and/or
+  modify it under the terms of the GNU General Public License as
+  published by the Free Software Foundation; either version 2 of the
+  License, or (at your option) any later version.
+
+  This program is distributed in the hope that it will be useful,
+  but WITHOUT ANY WARRANTY; without even the implied warranty of
+  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+  GNU General Public License for more details.
+
+  You should have received a copy of the GNU General Public License
+  along with this program; if not, write to the Free Software
+  Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
+*/
+
+#include "lib/error.h"
+
+CINELERRA_ERROR_DEFINE(TIME_OVERFLOW, "Time overflow");
+CINELERRA_ERROR_DEFINE(TIME_UNDERFLOW, "Time underflow");
+CINELERRA_ERROR_DEFINE(TIME_NEGATIVE, "Time negative");
diff --git a/src/lib/time.h b/src/lib/time.h
new file mode 100644
index 000000000..a2dea483b
--- /dev/null
+++ b/src/lib/time.h
@@ -0,0 +1,247 @@
+/*
+  time.h  -  Time calculations
+
+  Copyright (C)         CinelerraCV
+    2007,               Christian Thaeter <ct@pipapo.org>
+
+  This program is free software; you can redistribute it and/or
+  modify it under the terms of the GNU General Public License as
+  published by the Free Software Foundation; either version 2 of the
+  License, or (at your option) any later version.
+
+  This program is distributed in the hope that it will be useful,
+  but WITHOUT ANY WARRANTY; without even the implied warranty of
+  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+  GNU General Public License for more details.
+
+  You should have received a copy of the GNU General Public License
+  along with this program; if not, write to the Free Software
+  Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
+*/
+
+#ifndef CINELERRA_TIME_H
+#define CINELERRA_TIME_H
+
+#include <sys/time.h>
+#include <time.h>
+#include <math.h>
+
+#include "lib/error.h"
+
+/*
+  this time functions are small macro like wrapers, they are all inlined for performance reasons
+  time is passed around as pointers, this pointer must never be NULL
+
+  timehandling is a delicate business, be careful of precision errors accumulating, TODO explain how to use time
+
+*/
+
+/* over or underflow (tried to make a movie which has negative length? or more than some hundreds days?) */
+CINELERRA_ERROR_DECLARE(TIME_OVERFLOW);
+CINELERRA_ERROR_DECLARE(TIME_UNDERFLOW);
+CINELERRA_ERROR_DECLARE(TIME_NEGATIVE);
+
+/*
+  Note: we measure time starting from zero,
+  time never becomes negative
+  (I didnt checked if the time types are signed)
+*/
+typedef struct timeval cinelerra_time;
+typedef cinelerra_time* CinelerraTime;
+
+/**
+ * normalize time after operations.
+ * used internally
+ */
+static inline void
+cinelerra_time_normalize (CinelerraTime time)
+{
+  REQUIRE (time);
+  if (time->tv_usec >= 1000000)
+    {
+      time->tv_sec += (time->tv_usec / 1000000);
+      time->tv_usec = (time->tv_usec % 1000000);
+    }
+}
+
+
+/**
+ * set a time value to zero.
+ */
+static inline CinelerraTime
+cinelerra_time_clear (CinelerraTime time)
+{
+  if(time)
+    {
+      time->tv_sec = 0;
+      time->tv_usec = 0;
+    }
+  return time;
+}
+
+/**
+ * get current time.
+ */
+static inline CinelerraTime
+cinelerra_time_current (CinelerraTime time)
+{
+  if (time)
+    {
+      /* gettime should never ever fail in a correct program */
+      if (gettimeofday (time, NULL))
+        CINELERRA_DIE;
+    }
+  return time;
+}
+
+/**
+ * init from floating point representation.
+ */
+static inline CinelerraTime
+cinelerra_time_set_double (CinelerraTime time, double fp)
+{
+  if (time)
+    {
+      if (fp >= 0.0)
+        {
+          time->tv_sec = fp;
+          time->tv_usec = round((fp - time->tv_sec) * 1000000.0);
+          return time;
+        }
+      else
+        {
+          time->tv_sec = (time_t)-1;
+          time->tv_usec = (suseconds_t)-1;
+          cinelerra_error_set(CINELERRA_ERROR_TIME_NEGATIVE);
+        }
+    }
+  return NULL;
+}
+
+/**
+ * initialize with seconds and microseconds.
+ */
+static inline CinelerraTime
+cinelerra_time_init (CinelerraTime time, time_t sec, suseconds_t usec)
+{
+  if (time)
+    {
+      time->tv_sec = sec;
+      time->tv_usec = usec;
+      cinelerra_time_normalize (time);
+    }
+  return time;
+}
+
+/**
+ * get the seconds part from a time.
+ */
+static inline time_t
+cinelerra_time_sec (CinelerraTime time)
+{
+  if (time)
+    return time->tv_sec;
+  else
+    return (time_t)-1;
+}
+
+/**
+ * get the microseconds part of a time.
+ */
+static inline suseconds_t
+cinelerra_time_usec (CinelerraTime time)
+{
+  if (time)
+    return time->tv_usec;
+  else
+    return (suseconds_t)-1;
+}
+
+/**
+ * convert to floating point repesentation.
+ */
+static inline double
+cinelerra_time_double_get (CinelerraTime time)
+{
+  if (time)
+    {
+      double fp;
+
+      fp = time->tv_sec;
+      fp += time->tv_usec / 1000000.0;
+      return fp;
+    }
+  return NAN;
+}
+
+
+/**
+ * copy time
+ */
+static inline CinelerraTime
+cinelerra_time_copy (CinelerraTime dest, const CinelerraTime src)
+{
+  if (dest && src)
+    {
+      dest->tv_sec = src->tv_sec;
+      dest->tv_usec = src->tv_usec;
+    }
+  return dest;
+}
+
+/**
+ * add time.
+ */
+static inline CinelerraTime
+cinelerra_time_add (CinelerraTime dest, const CinelerraTime src)
+{
+  if (dest && src)
+    {
+      time_t t = dest->tv_sec;
+
+      dest->tv_sec += src->tv_sec;
+      dest->tv_usec += src->tv_usec;
+
+      cinelerra_time_normalize (dest);
+
+      if (dest->tv_sec < t)
+        {
+          cinelerra_error_set (CINELERRA_ERROR_TIME_OVERFLOW);
+          return NULL;
+        }
+    }
+  return dest;
+}
+
+/**
+ * substact time.
+ */
+static inline CinelerraTime
+cinelerra_time_sub (CinelerraTime dest, const CinelerraTime src)
+{
+  if (dest && src)
+    {
+      time_t t = dest->tv_sec;
+
+      dest->tv_sec -= src->tv_sec;
+      if (dest->tv_usec >= src->tv_usec)
+        dest->tv_usec -= src->tv_usec;
+      else
+        {
+          --dest->tv_sec;
+          dest->tv_usec += 1000000 - src->tv_usec;
+        }
+
+      cinelerra_time_normalize (dest);
+
+      if (dest->tv_sec > t)
+        {
+          cinelerra_error_set (CINELERRA_ERROR_TIME_UNDERFLOW);
+          return NULL;
+        }
+    }
+  return dest;
+}
+
+
+#endif
diff --git a/tests/10timefunctions.tests b/tests/10timefunctions.tests
index 764d91fd8..835e1a918 100644
--- a/tests/10timefunctions.tests
+++ b/tests/10timefunctions.tests
@@ -1,15 +1,126 @@
 
-TESTING "Time functions"
+TESTING "Time functions" ./test-time
 
-PLANNED "get time"
-PLANNED "add time, normalized"
-PLANNED "substract time, normalized"
+TEST "time init" init 15 500000 <<END
+out: 15 500000
+END
+
+TEST "time normalize" init 0 1500000 <<END
+out: 1 500000
+END
+
+TEST "time to float" todouble 15 500000 <<END
+out: 15.5
+END
+
+TEST "time to float, NULL gives a NaN" todoublenull <<END
+out: nan
+END
+
+TEST "float to time" fromdouble 33.6666666661 <<END
+out: 33 666667
+END
+
+TEST "float to time, round down" fromdouble 0.00000049 <<END
+out: 0 0
+END
+
+TEST "float to time, round up" fromdouble 0.0000005 <<END
+out: 0 1
+END
+
+TEST "current time" currenttime <<END
+return: 0
+END
+
+TEST "add time, normalized" add 1000001 2000002 <<END
+out: 3 3
+END
+
+TEST "substract time, normalized" sub 3000003 2000002 <<END
+out: 1 1
+END
+
+PLANNED "overflow"
+PLANNED "underflow"
+
+# frame 1 begins at time 0
+TEST "time to frame NTSC frame 1 begin" ntscframefromtime 0 0 <<END
+out: 1
+END
+
+# and ends at 33365
+TEST "time to frame NTSC frame 1 end" ntscframefromtime 0 33365 <<END
+out: 1
+END
+
+# thus 33366 is start of frame 2
+TEST "time to frame NTSC frame 2 begin" ntscframefromtime 0 33366 <<END
+out: 2
+END
+
+# and 66732 is the end of frame 2
+TEST "time to frame NTSC frame 2 end" ntscframefromtime 0 66732 <<END
+out: 2
+END
+
+# this makes 66733 the start of frame 3
+TEST "time to frame NTSC frame 3 begin" ntscframefromtime 0 66733 <<END
+out: 3
+END
+
+# after 1 hour we are at frame 107893
+TEST "time to frame NTSC after 1hour" ntscframefromtime 3600 0 <<END
+out: 107893
+END
+
+# after 200 days we are at frame 517881601
+TEST "time to frame NTSC after 200 days" ntscframefromtime 17280000 0 <<END
+out: 517882118
+END
 
 
-# the next ones for different common framerates, check corner cases
-PLANNED "time to frame"
-PLANNED "frame to time"
+TEST "frame to time NTSC frame 1" ntscframestart 1 <<END
+out: 0 0
+END
 
+TEST "frame to time NTSC frame 2" ntscframestart 2 <<END
+out: 0 33366
+END
+
+TEST "frame->time->frame conversion 2" ntscframecheck 2 <<END
+out: frame 2 1
+END
+
+TEST "frame->time->frame conversion 3" ntscframecheck 3 <<END
+out: frame 3 2
+END
+TEST "frame->time->frame conversion 4" ntscframecheck 4 <<END
+out: frame 4 3
+END
+TEST "frame->time->frame conversion 5" ntscframecheck 5 <<END
+out: frame 5 4
+END
+TEST "frame->time->frame conversion 6" ntscframecheck 6 <<END
+out: frame 6 5
+END
+TEST "frame->time->frame conversion 7" ntscframecheck 7 <<END
+out: frame 7 6
+END
+TEST "frame->time->frame conversion 8" ntscframecheck 8 <<END
+out: frame 8 7
+END
+TEST "frame->time->frame conversion 9" ntscframecheck 9 <<END
+out: frame 9 8
+END
+
+TEST "frame->time->frame conversion 100000" ntscframecheck 100000 <<END
+out: frame 100000 99999
+END
+
+TEST "frame->time->frame conversion 999999" ntscframecheck 999999 <<END
+out: frame 999999 999998
+END
 
 # how long are N frames on average (beware of precision!)
 PLANNED "frame duration"
diff --git a/tests/Makefile.am b/tests/Makefile.am
index 17f3ec7c5..dadee1385 100644
--- a/tests/Makefile.am
+++ b/tests/Makefile.am
@@ -18,10 +18,14 @@
 
 tests_srcdir = $(top_srcdir)/tests
 
-check_PROGRAMS += test-error
+check_PROGRAMS += test-error test-time
 
 test_error_SOURCES = $(tests_srcdir)/error/errortest.c
 test_error_CPPFLAGS = $(AM_CPPFLAGS) -std=gnu99 -Wall -Werror -I$(top_srcdir)/src/
 test_error_LDADD = $(builddir)/libcin3.a -lnobugmt -lpthread -ldl
 
+test_time_SOURCES = $(tests_srcdir)/time/test-time.c
+test_time_CPPFLAGS = $(AM_CPPFLAGS) -std=gnu99 -Wall -Werror -I$(top_srcdir)/src/
+test_time_LDADD = $(builddir)/libcin3.a -lnobugmt -lpthread -ldl -lm
+
 TESTS = $(tests_srcdir)/test.sh
diff --git a/tests/time/DIR_INFO b/tests/time/DIR_INFO
new file mode 100644
index 000000000..20a92392c
--- /dev/null
+++ b/tests/time/DIR_INFO
@@ -0,0 +1 @@
+test time and frame calculations
diff --git a/tests/time/test-time.c b/tests/time/test-time.c
new file mode 100644
index 000000000..519a65781
--- /dev/null
+++ b/tests/time/test-time.c
@@ -0,0 +1,147 @@
+/*
+  test-time.c  -  test time and framerate functions
+
+  Copyright (C)         CinelerraCV
+    2007,               Christian Thaeter <ct@pipapo.org>
+
+  This program is free software; you can redistribute it and/or
+  modify it under the terms of the GNU General Public License as
+  published by the Free Software Foundation; either version 2 of the
+  License, or (at your option) any later version.
+
+  This program is distributed in the hope that it will be useful,
+  but WITHOUT ANY WARRANTY; without even the implied warranty of
+  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+  GNU General Public License for more details.
+
+  You should have received a copy of the GNU General Public License
+  along with this program; if not, write to the Free Software
+  Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
+*/
+
+#include <stdio.h>
+#include <string.h>
+
+#include "lib/time.h"
+#include "lib/framerate.h"
+
+
+CINELERRA_ERROR_DEFINE(TEST, "test error");
+
+int
+main (int argc, char** argv)
+{
+  NOBUG_INIT;
+
+  if (argc == 1)
+    return 0;
+
+  if (!strcmp(argv[1], "init"))
+    {
+      cinelerra_time time;
+
+      cinelerra_time_init (&time, atol (argv[2]), atol(argv[3]));
+
+      printf ("%lu %lu\n", (long)cinelerra_time_sec (&time), (long)cinelerra_time_usec (&time));
+    }
+
+  if (!strcmp(argv[1], "todouble"))
+    {
+      cinelerra_time time;
+
+      cinelerra_time_init (&time, atol (argv[2]), atol(argv[3]));
+
+      printf ("%g\n", cinelerra_time_double_get (&time));
+    }
+
+  if (!strcmp(argv[1], "todoublenull"))
+    {
+      printf ("%g\n", cinelerra_time_double_get (NULL));
+    }
+
+  if (!strcmp(argv[1], "fromdouble"))
+    {
+      cinelerra_time time;
+
+      cinelerra_time_set_double (&time, atof (argv[2]));
+
+      printf ("%lu %lu\n", (long)cinelerra_time_sec (&time), (long)cinelerra_time_usec (&time));
+    }
+
+  if (!strcmp(argv[1], "currenttime"))
+    {
+      cinelerra_time time;
+
+      cinelerra_time_current (&time);
+
+      printf ("%lu %lu\n", (long)cinelerra_time_sec (&time), (long)cinelerra_time_usec (&time));
+    }
+
+  if (!strcmp(argv[1], "add"))
+    {
+      cinelerra_time time1, time2;
+
+      cinelerra_time_init (&time1, 0, atol (argv[2]));
+      cinelerra_time_init (&time2, 0, atol (argv[3]));
+      cinelerra_time_add (&time1, &time2);
+
+      printf ("%lu %lu\n", (long)cinelerra_time_sec (&time1), (long)cinelerra_time_usec (&time1));
+    }
+
+  if (!strcmp(argv[1], "sub"))
+    {
+      cinelerra_time time1, time2;
+
+      cinelerra_time_init (&time1, 0, atol (argv[2]));
+      cinelerra_time_init (&time2, 0, atol (argv[3]));
+      cinelerra_time_sub (&time1, &time2);
+
+      printf ("%lu %lu\n", (long)cinelerra_time_sec (&time1), (long)cinelerra_time_usec (&time1));
+    }
+
+  if (!strcmp(argv[1], "ntscframefromtime"))
+    {
+      cinelerra_framerate ntsc = {30000, 1001};
+      cinelerra_time time;
+
+      cinelerra_time_init (&time, atol (argv[2]), atol (argv[3]));
+
+      printf ("%lu\n", (long)cinelerra_framerate_frame_get_time (&ntsc, &time));
+    }
+
+  if (!strcmp(argv[1], "ntscframestart"))
+    {
+      cinelerra_framerate ntsc = {30000, 1001};
+      cinelerra_time time;
+
+      if(cinelerra_framerate_time_get_time_frame (&ntsc, &time, atol (argv[2])))
+        printf ("%lu %lu\n", (long)cinelerra_time_sec(&time), (long)cinelerra_time_usec(&time));
+    }
+
+  if (!strcmp(argv[1], "ntscframecheck"))
+    {
+      cinelerra_framerate ntsc = {30000, 1001};
+      cinelerra_time time1;
+      cinelerra_time time2;
+      cinelerra_framepos frame;
+
+      cinelerra_framepos frame1;
+      cinelerra_framepos frame2;
+
+      frame = atol (argv[2]);
+
+
+      if (cinelerra_framerate_time_get_time_frame (&ntsc, &time1, frame))
+        {
+          printf("frame %lu ", frame1 = cinelerra_framerate_frame_get_time (&ntsc, &time1));
+
+          cinelerra_time_init (&time2, 0, 1);
+          cinelerra_time_sub (&time1, &time2);
+          printf("%lu\n", frame2 = cinelerra_framerate_frame_get_time (&ntsc, &time1));
+          ENSURE (frame1 == frame2+1);
+        }
+
+    }
+
+  return 0;
+}
diff --git a/wiki/support_library.html b/wiki/support_library.html
index 6e8b5a717..144de95db 100644
--- a/wiki/support_library.html
+++ b/wiki/support_library.html
@@ -720,6 +720,19 @@ We use a common base class for all our application specific exceptions. These ex
 * getting standardized error messages automatically
 </pre>
 </div>
+<div title="FrameAndTime" modifier="CehTeh" modified="200708282024" created="200708261938" changecount="2">
+<pre>! Framerates
+Framerates are stored as rational numbers eg. 30000/1001 for NTSC, this representation allows highly precise integer calculations for frames and times.
+
+! Frames
+All calculations in cinelerra are based on frames which is a signed integer type. Together with a Framerate and a starting point, every frame can be exactly located.
+
+! Time
+Time is used only internally in cinelerra, every external representation of time will be converted to frames. Time has a precision of 1 microsecond and is stored in POSIX struct timeval. Time is always handled as absolute time, thus frame addresses map to absolute times, there is at worst a 1us precision jitter but no drift.
+
+!! SMPTE and other Timecodes
+will be added on demand, but be frame based, not time based</pre>
+</div>
 <div title="FullScreenPlugin" modifier="CehTeh" modified="200706110313" created="200607241016" tags="systemConfig lewcidExtension" server.type="file" server.host="file:///home/ct/.homepage/home.html" server.page.revision="200706110313">
 <pre>/***
 |Name|FullScreenPlugin|
@@ -2360,7 +2373,7 @@ h1,h2,h3,h4,h5,h6 {
 /*}}}*/
 </pre>
 </div>
-<div title="SupportLibrary" modifier="MichaelPloujnikov" modified="200707160346" created="200707102314" changecount="6">
+<div title="SupportLibrary" modifier="CehTeh" modified="200708261935" created="200707102314" changecount="8">
 <pre>The Support Library contains all tools we need at various places, but by themselves don't defines a subsystem on their own.
 
 These things are:
@@ -2369,7 +2382,7 @@ These things are:
 * a wrapper for POSIX Threads
 ** Thread creation joining and canceling
 ** Locking primitives like Condition variables and Mutexes
-
+* [[Frame and Time handling and calculations|FrameAndTime]]
  
 (... to be continued)
 </pre>